Imaging Canine Post-Trabecular Aqueous Outflow Pathways: Effect of Acute Intraocular Pressure Elevation in Normal...

Area of Science:

• Ophthalmology
• Veterinary Medicine
• Fluid Dynamics

Background:

• Intraocular pressure (IOP) is a critical factor in ocular health.
• The post-trabecular aqueous outflow tract's structural integrity is vital for maintaining normal IOP.
• Canine glaucoma research often focuses on trabecular meshwork dysfunction, with less attention to downstream pathways.

Purpose of the Study:

• To investigate the structural relationship between elevated intraocular pressure (IOP) and the post-trabecular aqueous outflow tract in canine eyes.
• To assess how acute IOP changes affect the morphology of the aqueous humor outflow pathways.
• To establish a baseline understanding of pressure-induced changes in canine ocular drainage.

Main Methods:

• Ex vivo canine eyes underwent concurrent aqueous angiography (AA) and anterior segment optical coherence tomography (OCT).
• Eyes were subjected to physiologic (10-25 mmHg) and elevated (55-68 mmHg) IOP for varying durations.
• Scleral lumen heights (SLH) were measured using OCT, and flow regions were characterized via AA.

Main Results:

• A significant correlation was observed between AA outflow signals and OCT-identified lumens at physiologic IOP.
• Elevated IOP led to a significant reduction in SLH (p < 0.0001) after 30 and 120 minutes.
• Vascular profiles appeared collapsed under elevated IOP, with larger vessels showing greater collapse.

Conclusions:

• Acute elevation of IOP causes significant structural collapse in the post-trabecular aqueous outflow pathways of healthy canine eyes.
• The reduction in SLH and high-flow regions suggests a pressure-dependent mechanism affecting aqueous humor drainage.
• Further research into these pressure-induced changes, particularly in glaucomatous canine eyes, is essential for developing novel diagnostic and therapeutic strategies.